Hard vegetable fiber product of high strength and process of making same



Jan. 2, 1934. 1 R BQEHM 1,941,536

HARD VEGETABLE FIBER PRODUCT OF HIGH STRENGTH AND PROCESS OF MAKING SAME Filed May 18, 1932 INVENT R ATTORNEY-5 Patented Jan. 2, 1934 PATENT OFFICE HARD VEGETABLE FIBER PRODUCT OF HIGH STRENGTH AND PROCESS OF MAK- ING SAME Robert M. Boehm, Laurel, Miss., assignor to Masonite Corporation, Laurel, Miss., a corporation of Delaware Application May 18, 1932. Serial No. 612,072

9 Claims.

My invention relates to hard, hot-pressed products, as for example boards, of vegetable fiber, and more particularly to such a board or other product having increased strength as measured, for example, by modulus of rupture. For convenience, I will refer to such products as board.

The objects of the invention include among others, the provision of a hard board or other 10 product, of vegetable fiber, that has high strength,

and at the same time is free from surface defects known as water spots, and the securing of high strength and high values of other valuable properties, such as water resistance, wet

strength, resistance to abrasion and the like in a hot-pressed vegetable fiber board by'relatively short time treatment, and without resort to pressures productive of undesiredly high density. Other objects will appear from the following description.

Vegetable fiber material for use with my invention may be obtained from various sources, such as hard woods, soft woods, wood forming grasses such as bamboo, cane, straw, or other fibrous vegetable material.

The preparation of the fiber can be accomplished in various ways in which the non-cellulose constituents are largely retained, as for example, by explosion or by grinding, or in other mechanical fashion, or by semi-chemical cooks, or partly by such cooks and partly mechanically, etc.

A raw fiber such as mechanically prepared or exploded fiber, or partially raw fiber such as semichemical fiber is preferred, not only on account of greater yield of board and relatively lower cost, but because of self-bounding properties due to retention of non-cellulose, high resistance to absorption of water and high wet strength, all of which are present to the greatest extent in the board made of the raw ligno-cellulose fiber, and to a considerable extent when the raw fiber is produced by semi-chemical cooks or by the combination thereof with mechanical treatment, etc.

The fiber is preferably refined as in a Clafiin, or rod-mill, or'other refiner, to a sufficient extent to be readily formed into a smooth blanket or wet-lap in a Fourdrinier or equivalent machine, and after such formation, preferably followed by passing through between press rolls, is made into a hard board by simultaneous application of heat and pressure, followed up as shrinkage occurs and maintained until the board is dry. In the case of making a board of about 1 specific gravity, and about one-eighth inch thick, at say 300 F. and a pressure of say 200 pounds per square inch, this requires about fifteen to twenty minutes.

A wire mesh screen is preferably interposed between one face of the board and a press platen to permit ready escape of moisture. The other surface is desirablya smoothly polished surface made, for example, against a smooth surface plate of chromium plated steel.

With raw ligno-cellulose fiber sufficiently refined to make a smooth wet-lap and introduced into the hot press when containing say 60% of water, if the pressure applied is sufllcient to give a board of such strength as to show a modulus of rupture as high as above 6,000, surface defects are likely to appear, especially on the smooth polished surface, that are known as water spots, and furthermore, the density will ordinarily exceed a specific gravity of 1, whereas, if the pressure be kept lower when it is desired to make a board of lower density, then, while the board will be free from water spot defects, it will be relatively lacking in strength.

By my invention, I obtain a board of strength materially over modulus of rupture 6,000, without so resort to pressures sufiicient to produce water spotting or give a high density, as for example,

I can secure such high strength in a board made under pressures giving a density considerably under specific gravity 1, which low density board is desirable for purposes where excessive weight and undue thinness are not wanted.

In carrying out my new process, I include or incorporate material adapted to impart high strength to the board or other product when same is subjected to a baking operation in presence of atmospheric or other oxygen, and I subject the board to such baking operation preferably by means of heated air and with provision for eflicient air circulation. Materials having drying characteristics can be used in. this way such as tung oil, linseed oil, and perilla oil, or mixtures thereof, or less preferably, materials such as rape oil, cottonseed oil, and the like may be used, preferably in admixture with the more desirable ma- 1 terials above referred to, or with admixture of suitable drying accelerators, and other materials operating in substantially'the same way can be used.

I purposely avoid inclusion or incorporation of 5 such materials or mixtures to such an extent as to produce saturation of the board, which, with a board of say 1 specific gravity, would require about 15% to 20% of the strength imparting material,

as tung oil for example.

This is not merely because of the economy so obtained in cost of materials, but because of the desirability of performing the baking operation so as to secure the highest strengthening effect inthe shortest practicable time, and therefore at the highest practicable temperatures. I find that if the drying oil or other strength imparting agent is present or incorporated to an extent at all approaching saturation, even though the surface excess thereof be wiped or otherwise removed from the surface of the board, when the board containing so much of the drying agent or the like is subjected to substantially high temperature for rapid baking, e. g. 300 R, an effect is quickly produced, which is apparently of a sealing character and productive of lack of access of atmospheric oxygen to the inner portion of the board. The result is that further baking, for any a softening action of the considerable percentage of tung oil or other material present in the board. By using a relatively small proportion of the material having drying characteristics, such as tung oil, for example, say 4% thereof, of the dry weight of fiber, I avoid producing such an oxygen excluding effect as just described, and perform the baking rapidly and efficiently and get good increase in strength in a short time without undue necessity of holding the baking temperature down.

The material having drying characteristics can be substantially uniformly distributed throughout the entire thickness of the board or other product, by introduction thereof into the pulp from which the fiber mass is formed. Such a board or other product is preferably waterproofed by incorporating a waterproofing agent such as rosin or a hydrocarbon material in the pulp. About 1 /g% of hydrocarbon material, such as petrolatum, is an effective waterproofing agent, and when the material that is used having drying characteristics is tung oil, for example, the petrolatum or other waterproofing material may be conveniently dissolvedin the tung oil and the mixture incorporated with the fiber in the mixing chest before being dewatered and formed into the fiber mass or wetlap from which the board is made by hot pressing, or the material with drying characteristics may be applied otherwise, as for example applied to the wet-lap after same is formed.

If it is desired to incorporate the entire content of strengthening agent, as'tung oil, in any of the foregoing ways, same may advantageously be about say 4% of the weight of dry fiber. It appears to be substantially entirely taken up by the fiber with little or no loss thereof during the dewatering and hot pressing operations.

An alternative way of introducing all or part of the strengthening material used is by impregnation treatment of the hard board, after same has been formed by hot pressing. This treatmentmay consist, for example of dipping or submerging the hard board in a bath of strengthening agent such as tung oil, followed by passing it through between high pressure rollers, which may be disposed below the surface of the bath if desired. Such roller treatment compresses the board progressively along a narrow transverse region and absorption of the treating material is believed to take place as the result of suction effect obtained by the expansion of the board after being subjected to such compression.

When the boards are smooth and polished on one face and contain a. wire mesh impression surface on the other face, the latter face will take up somewhat more of the treating material than tion of the tung oil or other material can be minimized or avoided.

I find that when using tung oil, it is desirable to incorporate about 5% of cottonseed oil therewith (i. e. 5% of the oil bath) in order to avoid a tendency of the tung oil to thicken up, particularly after being subjected to fairly high heating over a considerable period, as heating to around 150 R, which is desirable in order to secure good penetration of the board. If desired, a thinning and penetration-aiding material such as a light parafiln hydrocarbon may be incorporated in the bath, and may form up to about 50% of the treating bath.

The first described mode of including the strength giving agent in the fiber mixing chest is of advantage in securing uniform distribution throughout the thickness of the fiber mass and resulting board. The impregnation mode just described has the advantage that the inclusion of tung oil or other strength giving material is greatest at the surfaces and the resulting improvement upon baking in properties such as strength and hardness is likewise greatest at the surfaces, which are of course, exposed in use and should desirably have the best properties.

However, I have found that a combination of the two modes for inclusion of the strength giving material to be preferable, namely, by securing uniform distribution throughout the board or other body of one portion, preferably about onehalf of the strength-giving agent used, through preliminary incorporation thereof in the fiber, and incorporating the other portion, preferably approximately the remaining one-half, of the strength giving agent by the impregnation route. In this way, the central zone of the board will contain the strength giving material to some extent through the introduction of a part thereof into the fiber in which it was substantially uniformly distributed, and the parts adjacent to the surfaces, while containing same to an additional extent, do not carry all thereof, as may happen with impregnation alone.

To obtain increased strength by the inclusion or incorporation of material having drying characteristics, the board is baked in presence of oxygen as for example with free access of air, and the temperature may be adapted to the particular drying oil material used, as for example, when using tung oil, about 300 F. With this temperature and using about 5% of tung oil in a hard board of raw ligno-cellulose fiber of specific gravity about 1, the baking will be completed in about six hours, at which time without material density increase, the strength increase is notable and the modulus of rupture is frequently nearly doubled. With tung oil, the final hardening that is complete at the end of the baking period, is believed to be preceded by an intermediate polymerization which transforms the tung oil into substanough" acdess'of air-and hencegoxygen. It is 'de-- waste 7 "coats, of paint, varnish, enamel or-otherfinish getting a'good finish 'surface,f,and yet other features of advantage obtained;

tially a spongystate fayorable. to getting thor-f rel'ativelyl'esser degree.:-

J ri e preferably humidified 'to equalize its-moisture .content with atmospheric moisture and ,is ready for uses I The accompanying drawing comprises a series of curves. showing actual instances o fibakingx time, at atemperature of 300 .F.,- plotted against boards. ofraw ligno'-'cellulose'fiberof L02 specific gravity for 5%;

modulus-of rupture for and content of tung oil, and itwill-be noted that :inv 6 hours 5% of tung oilzitop curve) had its modulus of 'wasfrom 6150 to 7600p: 23%,

' a decrease ."in 6 hours rr'orn 6150 to 45900; or a rupture" increased from 6150 to substantially the v maximum for any time'period, .-namely 10,500,

' an increase of 13%;?11'161838 for 10% tung oil (middle curve) the increasezin strength in 6 hours "and furtherin- 'crease ,was .obtained only at the expense of very prolonged baking;

as represented by- 'rnodulus of rupture there was 3 decreased-4%. l

In addition tofsecurin g. a very desirable 115- crease in the strength and related properties of the board at substantially minimum expense for [material and treatment, with-absence of troubles from surface defects,'such as water'spots and the like, and without the, necessity of producing a -board of extremely highspeciflc gravity I also.

obtainfurther advantages by my invention as for example, an increasein tensile strength is obtained' to? approximately the ,same extent as that in modulus of rupture, and similar benefits obtainedinresistance to absorption of water, in

"wet strength andiri-flre1'resistance;"themodulus ot'elasticity is; materially increasedjand there.

"is a'itiemendous increase, amounting to practically five-fold, resistancetc abrasion.- A lso the appearance of the product is enhanced, less argument; or umps ha l (flit; 1134115316.";

times if desired and simi- .oil is tun'goil, the heated .bakingtlmethea board with the -rriaterialis subjected to sevenhours.

oil'is incorporated .into. before-itxis consolidated byheat and pressure. iand-for. 15 tung oil (lower-,- ,n i0st curve), instead of an increase of strength ingoil includes tung oil.

material: are required for great'dry andwet strength which comprises sub-- 1 jecting 'to' consolidating cien-tly large .non-cellulose content to bond the:

pressureand heat: until; 5' of vegetablefiber having asufiilus ofrupture of the material; r

2'.- ,The process of. claim 1' in which the drying air is at a temperature time during which the of about 300. FL, and'the heated air is less than is necessary tosaturate -the mass aftercdnsolidatiomto highly heatedzair fora suflicient time to greatly increase the modua drying'oil content the quantityofwhich is less than-one=half thatwhich The process or" claim 1 in which thedrying,

oil is tung oil oi the'weight of dry fiberi' 4.,The process of claim'l inwhich the drying thevegetable fibenmass to'theiextentof approximately 4% 5: -The processor claim 1 inwhich the drying oil isincorporate'dinto the vegetable fiber mate-- has been consolidated by heat and andthe likehaving-great dryv and wet strength and composed of V compressed vegetablw'fiber bonded together by non-cellulose and ahardened drying oil material in quantity less thanfpnehalf that whichfis necessary I I to saturate the come;- pressed'fibrous'materiaL; I 1

8. Theproduct of claim 7 in which'thedryin which the dry! ing oil is tung oil in quantity-of approximately 4%;0: the weight ofthe dry fiber.-

9. The product of claim ROBERT M. en-1M.-

ROBERT 130mm,. v

I lt i s hereby z e r-titiedthat errorqppearsih' v printed: specif ication of the 3 Above "numb'e red' -p a't,cn; requiring correction l5; fill lilvv s Page l li -3 v r l.-.

"sel -i-bounding"read seli bondingt and that thecaidLetters Patcn-tshoiildte aiuqiwi th rhis correction therein that thenme may-conform to the 'record' of the case in the Patcnt0ffice.

Sigue'd-and-sealed' this-27 th all of February,

r. was,

toting Commissioner; of Patents.

f1. The-process of making a-fiber product or 

